This study will investigate the occurrence and molecular characteristics of thyroid cancer in residents of the Bryansk Oblast of the Russian Federation who were up to 50 years of age at the time of exposure to radiation from the Chernobyl Power Station accident on April 26, 1986. The study has three primary purposes: 1) to characterize cases of thyroid cancer according to specific molecular markers of genetic change, and to investigate whether the presence of such markers is associated with individual thyroid radiation dose to the thyroid from the Chernobyl accident; 2) to investigate whether age-at-exposure dependent radiation dose response for thyroid cancer differs between cancers that are positive versus negative for the molecular markers investigated; and 3) to investigate whether the presence of these same molecular markers is associated with clinical outcome. Thyroid cancer cases diagnosed between April 1, 2001 and March 31, 2006 will be identified and the diagnosis confirmed by a panel of expert thyroid pathologists. Controls, equal in number to the cases of thyroid cancer, will be selected among residents in the Bryansk Oblast, without thyroid cancer, individually matched to cases by sex, age, type of settlement and talon. For all cases and controls, the following information will be collected: 1) demographic and health history; 2) details of residential and dietary history; 3) appropriate physical samples to aid dose reconstruction; and 4) a blood sample. Individual radiation dose to the thyroid will be estimated for each case and control. Paraffin embedded tissue or fresh frozen tissue will be obtained for each case to assess tyrosine kinase growth factor and tyrosine kinase receptor expression for purposes of estimating the association between the presence of each of the markers and individual thyroid radiation dose. Clinical history and outcome data will be collected from medical records for investigation of the association between adverse clinical outcome (e.g. recurrence) and individual thyroid radiation dose, patient characteristics, and molecular markers of genetic change. [unreadable] [unreadable]